Method and apparatus for inspecting or testing a sample by optical metrology

摘要

A sample (1) is inspected or tested by illumination in which a line of coherent radiation (2) is scanned across the sample (1) with zero shear in the direction of scan. Two laterally displaced images of the sample (1) are generated which are phase stepped by stepping or ramping the phase of one of the two images during each of the line scans so that successive lines are incremented in phase to encode temporally information about the sample in one frame. The encoded information is decoded by running a vertical convolution mask (17) over the encoded frame image.